The Advanced Television Systems Committee (ATSC) published a Digital Television Standard in 1995 as Document A/53, hereinafter referred to simply as “A/53” for sake of brevity. Annex D of A/53 titled “RF/Transmission Systems Characteristics” is of particular relevance to this specification, defining many of the terms employed herein. In the beginning years of the twenty-first century, efforts were made to provide for more robust transmission of data over broadcast DTV channels without unduly disrupting the operation of so-called “legacy” DTV receivers already in the field. These efforts culminated in an ATSC standard directed to broadcasting data to mobile receivers being adopted on 15 Oct. 2009. This standard, referred to as “A/153”, is also relevant to this specification, defining many of the terms employed herein. The data for concatenated convolutional coding are commonly referred to as “M/H data” in reference to the mobile and handheld receivers that will receive such data.
Both A/53 and A/153 are directed to 8-VSB signals being used in DTV broadcasting. A radio-frequency (RF) 8-VSB signal is transmitted by vestigial-sideband amplitude modulation of a single carrier wave in accordance with an 8-level modulating signal that encodes 3-bit symbols descriptive of 2-bit symbols of the digital data to be transmitted. The three bits in the 3-bit symbols are referred to as Z-sub-2, Z-sub-1 and Z-sub-0 bits. The initial and final bits of each successive 2-bit symbol of the digital information are referred to as an X-sub-2 bit and as an X-sub-1 bit, respectively. The X-sub-2 bits are subjected to interference-filter pre-coding to generate the Z-sub-2 bits, which Z-sub-2 bits can be post-comb filtered in a DTV receiver to recover the X-sub-2 bits. The Z-sub-1 bits correspond to the X-sub-1 bits. The Z-sub-0 bits are redundant bits resulting from one-half-rate convolutional coding of successive X-sub-1 bits to provide two-thirds-rate trellis coding as prescribed by A/53.
A/53 prescribes (207, 187) Reed-Solomon forward-error-correction (RS FEC) coding of data followed by convolutional byte interleaving before two-thirds-rate trellis coding that employs one-half-rate convolutional coding of the less significant bits of successive two-bit symbols of data. It is a common practice in the digital coding arts to precede convolutional coding by RS FEC coding and byte interleaving of the RS FEC codewords. In a receiver the decoding of the convolutional coding is apt to contain burst errors caused by the decoding procedures stretching response to bit errors. De-interleaving the burst errors breaks protracted burst errors up into isolated byte errors that can oftentimes be corrected in reliance upon the RS FEC coding. Usual practice is to complete decoding of the convolutional coding before subsequent de-interleaving, to break up burst errors into isolated byte errors, and decoding of the RS FEC coding, to correct the isolated byte errors if there are not too many per RS FEC codeword.
A/153 prescribes serial concatenated convolutional coding (SCCC) of data transmitted to mobile receivers, which SCCC uses one-half-rate outer convolutional coding upon such data followed by symbol-interleaving and two-thirds-rate trellis coding similar to that prescribed by A/53. The one-half-rate convolutional coding incorporated within the two-thirds-rate trellis coding serves as one-half-rate inner convolutional coding in the SCCC. A/153 further prescribes additional forward-error-correction coding of the data transmitted to mobile receivers, which additional FEC coding comprises transverse Reed-Solomon (TRS) coding combined with lateral cyclic-redundancy-check (CRC) codes to locate byte errors for the TRS coding. The TRS FEC coding helps overcome temporary fading in which received signal strength momentarily falls below that needed for successful reception. The strongest TRS codes prescribed by A/153 can overcome such drop-outs in received signal strength that are as long as four tenths of a second.
Since the adoption of A/153, some members of ATSC have expressed concern with the capability of transmissions made in accordance with A/153 having sufficient capability to overcome burst noise that is of shorter duration, but occurs frequently within an RS Frame. These ATSC members have suggested further error-correction coding of M/H data, designed to be decoded in the internet-protocol (IP) transport-stream (TS) packets recovered from the RS Frames in the so-called “physical layer” portion of an M/H receiver. The inventor points out that, because burst noise tends to align with the rows, row-wise FEC coding of M/H data from RS Frames is at a disadvantage compared to FEC coding that is transverse to those rows. This problem is mitigated a bit by the symbol interleaving associated with SCCC. But not a great amount, since SCCC is designed primarily for overcoming additive white Gaussian noise (AWGN) or the like and is not very effective at overcoming burst noise of considerable duration.
The principal design task for the transverse Reed-Solomon (TRS) coding used in the RS Frames prescribed by A/153 is overcoming drop-outs in received strength caused by reception nulls when the receiver is moved through an electromagnetic field subject to multipath signal propagation. However, the shortened 255-byte Reed-Solomon (RS) codes used for TRS coding are very powerful codes for correcting shorter burst errors, especially when used together with codes for locating byte-errors. If RS codes are relieved of having to locate byte-errors as well as correct them, they can correct as many byte-errors within each of them as each has parity bytes. If RS codes have to locate byte-errors as well as correct them, they can correct only one-half as many byte-errors within each of them as each has parity bytes. Providing a sufficient number of parity bytes in each RS code to implement the principal design task for TRS coding requires a significant investment in reduced M/H payload. The inventor's opinion is that care should be taken to maximize the return from that investment.
A/153 prescribes two-dimensional coding of RS Frames of randomized M/H data in which the bytes in each RS frame are cyclically redundantly coded row by row to form respective cyclical redundant code (CRC) codewords. These row-long CRC codewords can be used as error-locating codes for the TRS codewords, but only in common, on a collectively shared basis. This works reasonably well when overcoming protracted drop-outs in received strength caused by reception nulls when the receiver is moved through an electromagnetic field subject to multipath signal propagation. These protracted errors typically extend several rows of bytes in the RS Frame and affect all TRS codewords in the RS Frame.
Each occurrence of shorter burst noise is apt to affect only some of the TRS codewords in the RS Frame. Intermittent electrical arcing in the motors of household appliances or unshielded electrical ignition wiring of gasoline engines can cause such shorter burst noise. Several occurrences of such shorter burst noise are apt to occur in some RS Frames. The row-long CRC codewords will respond to each occurrence of shorter burst noise to locate a byte error in each and all of the TRS codewords in the RS Frame. Several occurrences of shorter burst noise in an RS Frame can cause the row-long CRC codewords to locate more possible byte-error locations than can be accommodated by a TRS decoder using a byte-error-correction-only decoding algorithm for correcting TRS codewords. The TRS decoder can be designed so as then to switch over to a byte-error-location-and-correction decoding algorithm for correcting TRS codewords. However, the byte-error-correction capability of the TRS decoder is halved by switching over to a byte-error-location-and-correction decoding algorithm.
A/153 prescribes that the M/H-service information be subjected to outer convolutional coding and symbol interleaving before encapsulation in 188-byte transport-stream (TS) packets called “MHE packets” that are subjected to non-systematic (207, 187) Reed-Solomon coding to generate selected segments of 8-VSB data fields. These segments of 8-VSB data fields are time-division multiplexed with other segments generated by systematic (207, 187) Reed-Solomon coding of 188-byte TS packets of main-service information. The bytes of the resulting 8-VSB data fields are convolutionally interleaved before being subjected to the ⅔ trellis coding that functions as inner convolutional coding of the CCC used for transmissions to M/H receivers. All the segments of 8-VSB data fields have (207, 187) Reed-Solomon coding to insure that DTV receivers already in the field continue usefully to receive main-service information.
Some of those “legacy” DTV receivers place themselves in a “sleeping” mode if their decoders for (207, 187) R-S coding find a large enough portion of the segments of 8-VSB data fields to contain byte errors that cannot be corrected. The non-systematic (207, 187) Reed-Solomon coding of MHE packets has commonly been regarded as a loss of digital payload that is unfortunately necessitated to accommodate these “legacy” DTV receivers.